1. The respiratory mechanisms of lampreys and hagfish differ based on their ecological niches, with lampreys using tidal ventilation and hagfish having internal gills. 2. Bony fishes generally have a double-pumping mechanism that allows for continuous water flow across the gills. Cartilaginous fishes like sharks have gills supported by gill rays and branchial arches. 3. Lungfish are closely related to the first land vertebrates and possess internal nostrils and lungs. They can breathe air via their lungs or water through their gills.

1. Respiratory System & Gas Bladder
Krishnendu Sinha
Assistant Professor
Department of Zoology
Jhargram Raj College
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Ventilation of Internal Gills: Agnathous

3. Myxine sp. (Hagfish)
• In lampreys and hagfishes the respiratory mechanisms are completely different based
on their ecological niche
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4. Single pump in Lamprey (Tidal ventilation)
Ventilation in the adult lamprey:
(a) Longitudinal section. Because the adult lamprey’s mouth
often is attached to prey, water must alternatively enter as
well as exit via pharyngeal slits. Thus, gill ventilation in the
lamprey, unlike most fishes, is tidal.
(b) (b) Frontal section of three gill arches. Double arrows
indicate tidal flow of water: black, inflow; gray, outflow.
(After Vertyebrates, Kardong, 6ed)
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Ventilation of Internal Gills: Bony Fishes

6. (After Comparative Physiology of Vertebrate
Respiration, Huges, 1965
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7. (c) Counter-current; (d) concurrent
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8. (c) Counter-current; (d) concurrent
(After Respiratory Physiology
of Vertebrates, Nilsson, 2010
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10. The operation of a double-pumping mechanism and the consequent
continuous flow across the gills make the terms inspiration and expiration
not entirely suitable.
These are applicable to tidal ventilation but for fish a subdivision of each
respiratory cycle into four parts is preferable
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Ventilation of Internal Gills: Cartilaginous fishes

12. Shark gill
(a) The interbranchial septum has banks
of lamellae supported by gill rays and a
medial branchial arch
(b) Structural units include a hemibranch
and a holobranch as well as a functional
respiratory unit
(After Vertyebrates, Kardong, 6ed)KS_JRC_Resp&GB

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Arial Respiration in Lung Fishes

15.  Lungfishes arose in the Devonian period
 They are closely related to the group of fishes (Crossopterygii) which gave rise to the first land vertebrates
 In common with crossopterygian fishes they possess internal nostrils which can be seen in the three living genera of
lungfishes
 These are found in the three southern continents and are Neoceratodus (Australia), Protopterus (Africa), and
Lepidosiren (South America)
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16.  Lungfishes arose in the Devonian period
 They are closely related to the group of fishes (Crossopterygii) which gave rise to the first land vertebrates
 In common with crossopterygian fishes they possess internal nostrils which can be seen in the three living genera of
lungfishes
 These are found in the three southern continents and are Neoceratodus (Australia), Protopterus (Africa), and
Lepidosiren (South America)
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17.  Only Neoceratodus is able to survive if it is not allowed to come to the surface and only this genus has well-
developed gill filaments
 The branchial arches of Lepidosiren pass through the gill arches with few capillaries and the blood does not
come into close contact with water
 In Neoceratodus the branchial arches break up into fine capillaries in the gills. It normally breathes under water
with the mouth slightly open and a current produced by slow movements of the two opercula
 This Australian lungfish rarely comes to the surface, but the other two genera regularly (e.g. every 15-30
minutes in Protopterus) come to the surface and gulp air through the mouth In fact only
 Protopterus makes a mud cocoon although Lepidosiren is also able to aestivate, but Neoceratodus cannot
survive out of water for long periods
 Protopterus may survive as long as 3-5 years in such a state
 Within the cocoon the O2 consumption falls by 50% during the first week and finally after several months to only
10% of its initial level
 Awakening from this remarkable state of dormancy is readily induced by the threat of asphyxiation.KS_JRC_Resp&GB

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Swim Bladder and the Origin of Lungs

19. Swim Bladder
Structure
• Two layers, tunica externa and tunica interna, are
usually distinguished
• The outer layer is often highly extensible and
consists of a trellis of elastic fibers
• The tunica interna has no elastic fibres but
contains collagen and smooth muscle
• In most swimbladders, two distinct vascularized
regions are recognized, one of which is ventral
and called the gas gland. Dorsally and posteriorly
is found the oval, so called because of its shape
when viewed from inside the bladder
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20. Structure
• Two layers, tunica externa and tunica interna, are
usually distinguished
• The outer layer is often highly extensible and
consists of a trellis of elastic fibers
• The tunica interna has no elastic fibres but
contains collagen and smooth muscle
• In most swimbladders, two distinct vascularized
regions are recognized, one of which is ventral
and called the gas gland. Dorsally and posteriorly
is found the oval, so called because of its shape
when viewed from inside the bladder
Swim Bladder
 Root Effect is the phenomenon where an
increased proton or carbon dioxide
concentration (lower pH) lowers
hemoglobin's affinity and carrying
capacity for oxygen
 The Root effect is to be distinguished from
the Bohr effect where only the affinity to
oxygen is reduced.
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21. Evolution of Lung
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22. Classification of (bony) fishes as per Young, 3rd edKS_JRC_Resp&GB

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24. Lung to Gas bladder Transition (Sagemehl Hypothesis)
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25. Graham et al. (19)
Evolution of Lung
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26. Daniels et al. (2004)
Phylogeny of Lung
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27. Evolution of gas bladders: Lungs, ventral in position, evolved in the common ancestor to actinopterygians and
sarcopterygians. Swim bladders in actinopterygians may have evolved independently, or they may have been
modified from earlier lungs. Some gas bladders are respiratory in function. Above the dendrogram outlining the
evolutionary rise of each group, there are sagittal (top) and cross-sectional (bottom) views of the lung and its
connection to the digestive tract. In Polypteriformes (Polypterus), paired lungs open through a common muscular
glottis into the right floor of the pharynx. The left lung is reduced, the right one long, but the epithelial lining of
both is smooth. Swim bladders of sturgeons originate from the stomach and those of primitive teleosts from the
esophagus, suggesting that these nonrespiratory gas bladders may be of independent origin in these two groups.
Dashed arrows indicate points where the respiratory function of the gas bladder is lost
Evolution of Gas Bladders
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28. Progressive Spatial Evolutionary Changes
of Lung/Gas Bladder in Respect to Gut
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References

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